This invention relates to a tracked multiple carrier transportation system. The system employs a series of linear induction motors spaced along a track. A plurality of carriers are used for moving objects through the system. A reaction plate is mounted on each carrier and acts as a secondary for the linear induction motors. The secondary is designed to interact with the two stator halves of the motor. The interaction between the reaction plate and the electromagnetic field generated by the linear induction motors produces a mechanical thrust which propels the carriers down the track.
Other similar transportation systems exist. In U.S. Pat. No. 3,803,466, issued to Ronald C. Starky on Apr. 9, 1974, a tracked vehicle propulsion system employs a plurality of linear synchronous motors. Trains of cars are mounted to ride along a track. Each car bears a linear rotor having interdigitated magnetic poles and is propelled by successive linear motors. Every motor, or thruster, is provided with thruster control that is connected to establish inter-thruster logic.
Unlike the subject invention, the velocity of the cars in the Starky patent is controlled by regulating the input frequency to the linear synchronous motors. Change in speed is achieved by sweeping the stator frequency from synchronism with one frequency to synchronism with another frequency. In the subject invention, the input frequency does not act as a control signal. A change in carrier velocity is achieved by regulating the input voltage to linear induction motors. The thrust produced is proportional to the square of the input voltage.
Another obvious difference between the subject invention and the Starky patent lies in the type of secondaries employed. The subject invention uses a reaction plate which is a flat piece of metal which interacts with the stators of the linear induction motors. In the preferred embodiment, the reaction plate is positioned to pass over the stators. The reaction plate can be made of a variety of metals, including brass, steel, copper and aluminum, or a combination of these materials. The electromagnetic forces induced from the stators (primary) to the reaction plate (secondary) produces energy in the form of electromagnetic thrust. The Starky patent discloses a similar thrust. However, that system utilizes a secondary consisting of interdigitated magnetic poles. This is clearly different than the present system and serves to highlight the differences between the two types of motors used.
Another transportation system is found in U.S. Pat. No. 4,348,618 issued to Nakamura et al. on Sept. 27, 1982. It deals with a feeding system for a linear motor transportation system. It employs a number of linear motors along a track to generate a moving magnetic field for driving trains.
Unlike the subject invention, however, the speed and acceleration of the train in the Nakamura patent does not play a part in the control logic. The linear thrusters are energized and de-energized depending solely on the presence or absence of the train.
In the subject invention, a control system utilizing a series of feedback loops and a central computer is employed to monitor and coordinate the movements of the carriers in the system. Each loop consists of a linear induction motor, a position sensor, a position indicator and a control module. The feedback loops are interconnected via the control modules which, in turn, are connected to the central computer.
As the carrier units pass by a linear induction motor, a position indicator which is attached to the carrier is read by a position sensor which is located near the linear induction motor. The sensor relays position information to the control module. The control module electronically determines the velocity and acceleration of the carrier. These values are then compared to a set of velocity and acceleration curves stored in module memory. Using the difference between the calculated and stored information, control signals are generated for increasing, decreasing or maintaining the strength of the powr input to the linear induction motor. Means for monitoring the power input to the motor, for reversing the sense of the power flow, and for disconnecting the power supply are all included in the control module. Accordingly, the position, velocity and acceleration of the carrier units are controlled by regulating the magnitude and sense of the power input to the various linear induction motors.
The thrust produced by a linear induction motor is proportional to the square of its input voltage. By increasing the power input, a greater thrust is produced. The force associated with this thrust translates into a proportional acceleration for the carrier. Deceleration of a carrier is achieved by reversing the direction of the input flow. This generates a thrust in a direction opposite to the movement of the carrier, thereby reducing the speed of the carrier. Once a desired velocity is achieved, the input to the induction motor, or motors, is held at a constant level.
If a current is passed through the stator windings of the linear induction motor in the absence of a secondary, there is the possibility that the coils will burn out due to the high currents generated. Thus, each control module contains a means for disconnecting the power input supply should dangerously high currents in the motor develop or should the position sensor detect the absence of a carrier unit.
In the subject invention, the linear induction motors are positioned along the track to provide continuous electromagnetic contact with the carrier reaction plates. As a reaction plate leaves the influence of one induction motor, it is simultaneously entering the field generated by a subsequent motor.
A variety of position sensors and indicators may be employed in this type of system. For instance, an induction transducer and a series of equally spaced magnetic strips may be used. Similarly, an optical sensor and bar code could also be used. In fact, any suitable system capable of transmitting and receiving position information can be employed. The system, however, must be capable of sensing the presence or absence of the carriers, identifying each unit, and transmitting and receiving information capable of being transformed into velocity and acceleration data.
Overall system logic is established through the use of a central computer. The computer functions to monitor and regulate the operation of the entire system. It should be capable of keeping track of each unit in the system. The desired position, velocity and acceleration of each unit, at each point in the system should also be programmed into the central computer. The computer acts to alert the individual control modules to this information, and directs them to generate control signals for keeping the system running smoothly. The information received by the computer from the various control modules may be relayed to subsequent control modules, thus coordinating the various feedback loops.
Other embodiments are possible. For example, the intelligence of the control module could be incorporated into the central computer.